lecture 21- animal nutrition and digestion

Question 1

Describe intracellular digestion

Answer 1

Amoeba surround food via pseudopods - finger-like projections

Food is engulfed

Termed phagocytosis

Question 2

Describe carbohydrate digestion

Answer 2

Main types

Fructose, glucose, galactose (monosaccharide)
Sucrose and lactose (disaccharides)
Complex: Starch and glycogen (polysaccharides)

Enzymes

Salivary amylase (mouth)
Pancreatic amylase (duodenum) -> di-, tri-, oligosaccharides

Brush border enzymes (enterocytes) -> monosaccharides

Question 3

Describe the polysaccharides of alpha glucose

Answer 3

Amylose - joined by alpha 1-4 glycosidic bonds - linear chain

Amylopectin - also has 1-6 bonds

Glycogen - many more 1-6 bonds

Amylase only breaks 1-4 bonds so amylopectin and glycogen need further processing

Question 4

Describe the brush border enzymes

Answer 4

Maltase splits maltose into 2 glucose molecules

Sucrase breaks disaccharide sucrose into glucose and fructose

Lactase hydrolyses lactose into glucose and galactose

Question 5

Describe carbohydrate absorption

Answer 5

Monosaccharides absorbed by facilitated diffusion and cotransport

Cotransport (with sodium ion) for glucose and galactose uptake

Facilitated diffusion for fructose uptake - GLUT5, requires diffusion gradient

Diffusion through basolateral surfaces by facilitated diffusion via GLUT2

Sodium ion concentration low in the cell

• Na+ out in exchange for K+
• drives Na+ into cell down gradient shuttling glucose/galactose into cell

Question 6

Describe protein digestion and absorption

Answer 6

Proteins either ingested or from cell breakdown
Digested by endo and exopeptidases

Endo: split polypeptides at interior bonds
Exo: cleave terminal amino acids

Begins in stomach

	Pepsinogen  ->  Pepsin   ~pH 2 pepsinogen is inactive precursor of pepsin

Question 7

Describe the role of chief cells

Answer 7

secrete pepsinogen

Question 8

Describe the role of parietal cells

Answer 8

secrete acid - keeps pH low to kill bacteria and create optimal environment for pepsin

Question 9

Describe how proteins are absorbed

Answer 9

Digestion in duodenum (upper part of small intestine)

	Trypsinogen -> Typsin     ~pH 7 Ttrypsinogen travels to small intestine as inactive form and is activated there

Brush border enzymes activated by typsin

Amino acids and peptides absorbed via cotransport

Question 10

Describe fat digestion

Answer 10

Triglyceride broken down into monoglyceride and 2 fatty acids

Lipases water soluble

Digestion requires bile salts (secreted from liver) - into gall bladder where it is stored

Form an emulsion in duodenum

Question 11

Describe fat absorption

Answer 11

Diffusion into enterocyte is passive - requires concentration gradient

In the cell, they combine to form triglycerides (in ER)

Packaged into chylomicrons (golgi apparatus)

Leave via exocytosis and enter circulation via lacteals

Chylomicrons too big to enter blood - enter lymphatic system which eventually drains into blood

Question 12

What are the problems with eating only plants?

Answer 12

Plants made of the polysaccharide, cellulose

Repeating D-glucose units linked with β1-4 bonds

Digested by cellulase which animals do not have

Question 13

How do some animals survive eating only plants?

Answer 13

Herbivores have bacteria which break down cellulose

Example of a symbiotic relationship

Bacteria produced in rumen and reticulum (stomach) of ‘foregut fermenters’

Hindgut fermenters produce bacteria in cecum
Less efficient - lots of digestion will have already taken place

Question 14

What are factors which affect absorption at the small intestine?

Answer 14

Factors which affect absorption:

Length

Surface area

Invaginations

Folding

Speed of passage